GB2053396A

GB2053396A - Proportioning valve for brakes reducing valve

Info

Publication number: GB2053396A
Application number: GB8021477A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1979-07-11
Filing date: 1980-07-01
Publication date: 1981-02-04
Also published as: GB2053396B; FR2460819B1; DE2927902C2; FR2460819A1; IT1131934B; IT8023336A0; US4335922A; DE2927902A1; JPS5650838A

Description

1

SPECIFICATION Pressure control unit

The. present invention relates to a pressure control unit, in particular for motor vehicle brake systems, said pressure control unit lying in the pressure medium connection between a master cylinder and at least one slave cylinder and comprising at least one differential piston, which is provided with a pressure medium passage, arranged in a housing and acted upon by the force of a control spring, and a valve which is operable in dependence on the displacement of the differential piston.

Such a pressure control unit is disclosed in US Patent Specification No. 3,727,989. However, the 80 known pressure control unit is characterized by a long constructional length and a heavy weight.

Further, the machining and assembly of the pressure control unit are very extensive as the bore which is stepped several times has to be made from two sides, the assembly of the individual parts being also effected from two sidds. This also implies the need of inserting an additional closure member with seals.

According to this invention there is provided a 90 pressure control unit, for a motor vehicle brake system in which said pressure control unit will lie in the pressure medium connection between a master cylinder and at least one slave cylinder, the unit comprising at least one differential piston, 95 which is provided with a pressure medium passage, arranged in a housing and acted upon by the force of a control spring, and a valve which is operable in dependence on the displacement of the differential piston, the valve closure member 100 being elastically supported, the differential piston comprising a hollow cylinder slidably sealed in a bore of the housing, on the one hand, and -a spigot, on the other hand, said spigot being fixed to the housing and projecting into the bore of the hollow 105 cylinder, and having a pressure medium inlet port, the differential piston having a radially inwards pointing collar which separates an inlet chamber from an outlet chamber, the valve closure member being arranged on the end of the spigot pointing 110 towards the collar. Three embodiments of the invention will be described in more detail in the following, reference being made to the drawing, wherein 50 Figure 1 shows a longitudinal section through a 115 pressure c6ntrol unit according to a first embodiment; Figure 2 shows a longitudinal section through a pressure control unit with adjustable control force (second embodiment); and Figure 3 shows a longitudinal section through a pressure control unit for a vehicular brake system wherein a first brake circuit is associated with the front wheels, a second brake circuit being associated with the rear wheels, (third embodiment).

In Figure 1, a housing 1 is represented which is provided with a bore which is stepped several times, the narrow end of the bore being designed GB 2 053 396 A 1 as pressure medium connection 2 for a slave cylinder and the large end of the bore having a closure member 3. The closure member 3 may be secured to the housing 1 e.g. by means of caulking. The bore of the housing 1 accommodates a differential piston 4 which essentially has the design of a U-shaped hollow cylinder. The end of the differential piston 4 which is adjacent to the pressure medium connection 2 is guided in the bore of the housing and sealed by means of a seal 5. The other end of the differential piston 4 is guiddd on a spigot 6 designed to form part of the closure member 3 and pointing into the bore of the housing and is sealed against the spigot 6 by means of a seal 7. - On its end which is adjacent to the pressure medium connection 2, the differehtial piston 4 has a radially inwards pointing collar 8 which defines a pressure medium passage 9. On the side"of the collar 8 facing the spigot 6, an annular valve seat 10 is arranged. The spigot 6 has an extension 11 on its free end, on said extension 11 an annular valve closure member 12 being slidably arranged in a sealing manner. At the free end of the - extension 11 a ring 13 is fastened which serves as stop of the valVe closure member 12 and against which the valve closure member 12 is loaded by means of a spring 14 supported at the front face of the spigot 6.

The closure member 3 has a second spigot 15 which is pointing axially outwards and which is provided with an external thread 16. A pressure medium channel 17, 17 extends through the closure'member 3 and its two spigots 6 and 15, passing through a cross hole 18 in the extension 11 and ending in an inlet chamber 19 of the pressure control unit. Due to the specific design of the closure member 3 by providing it with the second spigot 15 and its thread 16, the pressure control unit is particularly suitable as sprew-in cartridge, e.g. for being screwed into the pressure medium connection of a master cylinder.

The front face of the differential piston 4 which faces the pressure medium connection 2 confines a pressure outlet chamber 20. Between the housing 1 and the spigot 6 and between the housing 1 and a portion of the differential piston 4, respectively, an annular chamber 21 is formed which accommodates a control spring 22 which supports itself at the closure member 3, on the one hand, and at a radially outwards pointing collar 23 of the differential piston 4, on the other hand.

The mode of operation of the pressure control unit represented in Figure 1 is described as follows- In the rest position of the arrangement, the two moving parts, i.e. the differential piston 4 and the valve closure member 12 will be in the represented positions. If in the inlet port a pressure is built up pressure medium will flow through the pressure medium channel 17, 17, the cross hole 18, and the pressure medium passage 9 to the pressure medium connection 2 whence it will proceed to the slave cylinder.

2 GB 2 053 396 A 2 On a certain pressure level, due tb the pressurized surfaces of the differential piston 4 which are varying in size, a force difference will become effective which will displace the differential piston 4 against the force of the control spring 22. This movement of the differential piston 4 will cause the valve seat 10 to abut the valve closure member 12 and to thus close the pressure medium passage 9.

A further increase in pressure in the master cylinder will result in a reduced pressure increase in the slave cylinder in correspondence with the surface-ratio of the front face of the differential - piston 4 confining the inlet chamber 19 relative to the surface of the differential piston 4 confining the outlet chamber 20.

If in the inlet port the pressure is reduced to the effect that the inlet pressure will be lower than the outlet pressure then the valve closure member 12 Will move against the spring 14 due to the force 85 difference resulting from the different pressures and will thus lift off the valve seat 10 in consequence whereof the pressure medium passage 9 will be open again. Thus the pressure between the slave cylinder and the master cylinder will again be compensated.

In Figure 2, a pressure control unit is represented whose essential components correspond to the subject matter of Figure 1. In order to avoid repetitions, the following. 95 description will only deal with the differences in respect of the subject matter of Figure 1. The same parts will thus have the same reference numerals.

In this embodiment a cone valve 24 is provided 100 as valve closure member, said cone valve 24 supporting itself at the front face of the housing 1 by means of a tappet 25. A spring 14 supports the cone valve 24 at the spigot 6. In order to level up the change-over point of the pressure control 105 valve a second control spring 26 is provided in addition to control spring 22.

The housing _1 is thinwalled in its area which accommodates the closure member 3. By means of projections 27, the housing 1 engages a radial 110 recess 28 of closure member 3. This arrangement enables the control force to be adjusted, the assembly being easy. To this end, the closure member 3 is inserted into the bore of the housing 1 with the originally plane housing wall and is displaced in the direction of the control springs 22 and 26, thereby loading these springs. As soon as these springs will have been preloaded with the desired force, in the area of the radial recess 28, the thin-walled portion of the housing will be pressed into this groove, thus the projections 27 being formed.

The adjustability of the force is possible because of the length of the tappet 25 determining the valve closing distance. Thus the valve closing distance is independent of the position of the closure member 3 relative to the housing 1. Due to the small closing distance tolerances, this embodiment is particularly suitable for twin control units.

The mode of operation of the pressure control unit represented in Figure 2 is as already described with reference to Figure 1.

In Figure 3, a pressure control unit is represented for a two-circuit vehicular brake system, the first brake circuit being associated with tile front wheels and the second brake circuit being associated with the rear wheels. In this embodiment, the right-hand portion of the pressure control unit resembles the arrangements in Figures 1 and 2 very much. For the sake of avoiding repetitions, here, only the differences in respect of the pressure control units described above will be pointed out. The same parts will have the same reference numerals.

A poppet valve 29 is provided as valve closure member. Said poppet valve 29 has a tappet 25 projecting through the pressure medium passage 9 into the outlet chamber 20 where it is supported at a stop means. A master cylinder Hz 11 is connected to the inlet channel 17, the wheel cylinders of the rear wheel brakes HA being connected to the pressure medium connection 2.

In the left-hand portion of the housing 1, a second bore is provided whose end has a thread into which a screw plug 30 is screwed. The stepped bore accommodates a stepped piston 3 1, 31 which is sealed against the housing 1 by means of seal 32, 33, and 34. The largef portion of the piston 31 confines a pressure cha - mber 35 by means of its front " face which is facing the smaller piston portion 3 1, in said pressure - chamber 35 a pressure medium connection 36 ending which is connected with a brake circuit VA acting on the front wheels. Between the larger portion of the piston 3 1 and the screw plug 30, a helical compressing spring 37 is inserted which preloads the piston 31, 31 in the direction of the pres sure chamber 35. At the free end of the smaller portion of the piston 31, a pin 38 is arranged which projects through an opening in the housing into the pressure outlet chamber 20 and which is resting against the tappet 2 5 of the poppet valve 29. Between the seats 33 and 34, the piston 31 has an annular chamber 39 which is communicating with the atmosphere via an opening 40 of the housing 1.

Provided the brake circuit.acting on the front wheel brakes VA is intact, the piston 31 will be displaced against the force of the helical compression spring 37 upon a pressure built up by the master cylinder Hz 1, the pin 38 being drawn out of the outlet chamber 20. The tappet 25 of the poppet valve 29 now will abut the wall of the housing. The poppet valve 29 will be in the socalled ready position, i.e. upon a corresponding displacement of the differential piston 4, the valve will be closed.

Upon failure of the brake circuit Hz 1 acting on the front-wheel brakes VA, the force of the helical compression spring 31 will keep the piston 31, 31 in its rest position, the pin 38 keeping the poppet valve 29 in a position which will prevent the valve from closing even upon a maximu-m displacement of the differential piston 4. This - 'i T 1 i R 3 GB 2 053 396 A 3 arrangement serves the purpose of ensuring that, 2. A pressurei control unit as claimed in claim 1, upon failure of the front axle brake circuit VA, the 40 wherein the pressure medium passage is axially rear axle brake circuit HA will be supplied with a braking pressure which will not be reduced.

Advantages of the pressure control unit desribed in particular are to be seen In the fact that a) the pressure control unit has a short constructional length and a low weight; b) the pressure control unit comprises just a few components which are easily machined and assembled, thus the costs of manufacture being kept to an extremely low level; c) the pressure control unit is marked by an extreme operational reliability.

Claims

1. A pressure control unit, for a motor vellcle brake system in which said pressure control unit will lie in the pressure medium connection between a master cylinder and at least one slave cylinder, the unit comprising at least one differential piston, which is provided with a pressure medium passage, arranged in a housing and acted upon by the force of a control spring, and a valve which is operable in dependence on the displacement of the differential piston, the valve closure member being elastically supported, the differential piston comprising a hollow cylinder slidably sealed in a bore of the housing, on the one hand, and on a spigot, on the other hand, said spigot being fixed to th6 housing and projecting 70 into the bore of the hollow cylinder, and having a pressure medium inlet port, the differential piston having a radially inwards pointing collar which separates an inlet chamber from an outlet chamber, the valve closure member 75 being arranged on the end of the spigot pointingtowards the collar.

arr anged in the collar which is designed as valve seat.

3. A pressure control unit as claimed in claim 1 or 2, wherein the valve closure member is sealingly guided on an extension of the spigot and is loaded by a spring against a stop ring fastened -at the free end of the extension.

4. A pressure control unit as claimed in claim 1 or claim 2, wherein the valve closure member is a cone valve or poppet valve arranged between the collar and the spigot, spring-loaded in the direction of the collar, and supported by a tappet at a stop which is fixed to the housing.

5. A pressure control unit as claimed in claim 4, wherein the cone valve or the poppet valve may be brought into its open position by means of a device operated in dependence on the pressure of a second hydraulic circuit.

6. A pressure control unit as claimed in any one of the preceding claims, wherein the spigot is part of a closure member of the housing.

7. A pressure control unit as claimed in any one of the.preceding claims, wherein the control spring at least partially surrounds the differential piston in a coaxial manner.

8. A pressure control unit as claimed in claim 7, wherein the differential piston has a radially outwards pointing collar, the control spring bearing on said collar.

9. A pressure control unit substantially as described with reference to Figure I or Figure 2 or Figure 3 of the accompanying drawings.

10. A vehicle brake system having a unit according to any preceding claim in the pressure connection between the master cylinder and the slave cylinder.

Printed for Her Majesty's Stationery Office by the Courier Press, Lemington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.